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USB 3.2: The Basics

Like Goldilocks we know when something is just right. Not too big, not too difficult, not too hot or cold (as in porridge). When it isn’t we don’t hide our displeasure. But the recent announcement from the USB Promoter Group— which counts Apple, HP, Intel, Microsoft and Texas Instruments among its members— regarding the upcoming USB 3.2 standard seems “spot on,” as my British friends might put it. So without delay here’s the good news: USB transfer speeds will double (up to 20Gb/s) and if you have a USB Type-C cable certified for 10Gb/s “SuperSpeed+” there’s no need for new cables.

At the risk of oversimplification this is what’s happening: USB-C cables are able to connect to various interfaces by having four pairs of wires, or "lanes," to transfer data. But the current USB 3.1 spec doesn't allow USB-C cables to transfer data over multiple lanes simultaneously. USB 3.2, according to the USB Promoter Group, will do exactly that. With USB 3.2, hosts and devices can be created as multi-lane solutions, allowing for either two lanes of 5Gb/s or two lanes of 10Gb/s operation while also remaining backwards-compatible with earlier USB devices.

There is one caveat: For users to obtain the full benefit of this performance increase, devices on both ends of the cable must be able to support those speeds; a new USB 3.2 host must be used with a new USB 3.2 device and the appropriately certified USB Type-C cable (as mentioned earlier in order for it to support these new transfer speeds, the cable needs to be Superspeed+ certified).

By way of review the numbered USB designations represent revisions that have been made over the years. USB 1.1 was the first to be commercially available in 1998, USB 2.0 arrived a couple of years later, and since then we’ve seen USB 3.0, USB 3.1 Generation 1, and USB 3.1 Generation 2, the last two boasting speeds of 5Gbps and 10Gbps, respectively.

Permit me a slight digression. Just so we are clear, USB 3.2 and USB Type C are not the same thing. USB 3.2 works with USB Type C connectors, and so does USB 3.1. USB 3.2 technology defines how data is sent over cables while USB-C technology is a physical specification that defines what the plugs and wires look like. Assuming the host and recipient devices are compatible with USB 3.2, it will be faster than USB 3.1, while remaining compatible with USB 3.0.

If you have hardware that supports it, you should be able to use your existing cable and that is the primary advantage of USB: it is a comprehensive standard. Almost every modern electronic device is equipped with some sort of USB I/O.

Another piece of good news concerns charging speeds. USB-C long been touted as the universal standard that can charge your phone, laptop or tablet, or your Bluetooth speaker, all through a single common port. In 2014 the maximum power output through USB cable was increased from 10 to 100 watts when the reversible C type plug was introduced. It’s to be expected that USB 3.2 also will bring an improvement in the charging department. Simply put, devices that charge via USB 3.2 can be expected to charge faster.

Even with its increase in speed USB 3.2 will not be the fastest port available on a computer today. That distinction remains with Thunderbolt 3 (Thunderbolt being the brand name of a hardware interface developed by Apple and Intel), which can use the same reversible connector at speeds of up to 40Gbps. There is, however, a stipulation:: Thunderbolt 3 passive cables have maximum lengths. 40Gbps of bandwidth is available as long as the cable is 0.5m (1.6 ft.) or shorter. Active Thunderbolt 3 cables with clock and data recovery chips inside can support 40Gbps data transfer at lengths of up to 2m. Thunderbolt 3 can use all four lanes for power but is limited to the more expensive active cables to retain the 40Gbps speed. Passive cables enable a top speed of 20Gbps. So Thunderbolt 3 at its best is faster than USB 3.2 and uses the same port type as USB-C so Thunderbolt 3 cable will work as a USB-C cable, but USB is available on many more devices.

In summary, then, key characteristics of the USB 3.2 solution are:

Two-lane operation using existing USB Type-C cables.

Continued use of existing SuperSpeed USB physical layer data rates and encoding techniques.

A minor update to hub specifications (a USB hub is a device that expands a single port into several so that there are more ports available to connect devices to a host system) is expected to address increased performance and assure seamless transitions between single and two-lane operation.

Branding and marketing guidelines will be established after the final specification is published. We do know you'll need a new device that supports USB 3.2 in the first place. The first USB 3.2 products can be expected by the end of this year but most hardware makers aren't expected to roll out product until the middle of next year at the earliest.

The USB 3.2 specification is now in a final draft review phase with a planned formal release in time for USB Developer Days North America, scheduled for September 26-27, 2017. This event is an excellent chance to learn more about USB 3.2, USB Type-C Cables and Connectors, USB Power Delivery and USB Type-C Authentication. It will take place at the Hyatt Regency Vancouver. Registration closes on Friday, September 15 at 5:00PM US Pacific Time.

Murray Slovick

Murray Slovick is Editorial Director of Intelligent TechContent, an editorial services company that produces technical articles, white papers and social media posts for clients in the semiconductor/electronic design industry. Trained as an engineer, he has more than 20 years of experience as chief editor of award-winning publications covering various aspects of consumer electronics and semiconductor technology. He previously was Editorial Director at Hearst Business Media where he was responsible for the online and print content of Electronic Products, among other properties in the U.S. and China. He has also served as Executive Editor at CMP’s eeProductCenter and spent a decade as editor-in-chief of the IEEE flagship publication Spectrum.